lmcke169, we generally don't take action if you have cheats installed, but do not use them. You could, in theory, have the x-ray installed and as long as you do not use it, we won't ban you for it.
That being said, we *CAN* tell if x-ray has been used. There are a number of methods, including patterns, logs, and statistical analysis, which we use to determine if a player has been x-ray mining and use to take appropriate action; It doesn't matter much which methods are used, we're more than happy to use all that are necessary to figure out what was going on. I would highly advise that you uninstall the mod while playing on our servers, as too often have people fallen for the temptation of hitting the key to turn it on. The laziness of not uninstalling it when you join our server is not worth the risk of getting banned from the community. I have personally seen Yield's abilities at finding and detecting x-ray mining, and they are not to be trifled with.